I have a 20 gallon tank which I am going to stock with my male betta and 4-6 cories. I would really like to have a few more fish though to add a little more excitement to the tank. What fish, if any, could live peacefully in a 20 gallon with a betta and cories?

I don't want there to be any chance for fin nipping since my betta's fins are very delicate and he is prone to fin rot so I don't think fish like tetras would work. I also don't want any more bottom feeders since I will be getting corydoras. Since I am inexperienced with fish, I want something that is easy to care for and I won't get any more fish if there's a chance of overstocking. Are there any fish that would work for my tank?

I've had one male Betta in a tank with Pearl Danios but I think Glofish might be a bit too bright. The trouble with Danios is they are also top dwelling fish and extremely active. Danios like strong currents too. The Betta I had with them was very docile. If you like Danios though pick a short fin variety and a muted color. I have a video of my 40g in Aquariums Tab if you want to see how active Danios are. You can see in the video how they like to play in the current from the return on my filter. I have Glofish aka Zebra Danios. You could go with Rasboras. I've always heard they are good with Bettas and not known to be fin nippers. They are easy to care for and there are a few choices on colors as well.

Danios and Glofish are the same thing, they were just mutated with color. And they need a tank that's at least 2-4 feet long, needy fish. :p You want middle dweller fish..? Betta on the top, catfish on the bottom. Hm... Tetras are your best bet, different kinds but still. I have no idea.

Danios and Glofish are the same thing, they were just mutated with color. And they need a tank that's at least 2-4 feet long, needy fish. :p
You want middle dweller fish..? Betta on the top, catfish on the bottom. Hm... Tetras are your best bet, different kinds but still. I have no idea.

Tetras are a good choice. Platys can be iffy, as are danios. Some bettas do not mind, but some fish... can be rightfully mean! Harlequins are good, and 8 would be a good number. Just remember to add high and low plants, along with hide holes at all levels (use of taller ornaments, caves for the bottom, etc)